Adjustable voltage autotransformer



.Fan. 31, 1967 A. R. PERRINS ADJUSTABLE VOLTAGE AUTOTRANSFORMER 2 Sheets-Sheet 1 Filed June 24, 1964 05 2/5 INVENTOR. Al Zel? E. Fer/ 075' flTTOI YJ m M 3% Z 5 w I Z Jan. 31, 1967 A. R. PERRINS 3,302,098

ADJUSTABLE VOLTAGE AUTOTRANSFORMER Filed June 24, 1964 2 Sheets-Sheet 2 O TO OOOOOO INVENTOR.

A Z Zen E. Per/"4W5 JqTTOK A EYS United States fatent C 3,302,098 ADJUSTABLE VOLTAGE AUTOTRANSFORMER Allen R. Perrins, Cheshire, Comp, assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed June 24, 1964, Ser. No. 377,584 12 Claims. (Cl. 323-435) The present invention relates to an autotransformer in which the output voltage may be substantially steplessly adjusted in value and more particularly to such a device in which the output voltage is adjusted by the sliding movement of a brush on a commutating surface formed on the autotransformer.

In the type of adjustable voltage autotransformer to which the present invention is applicable, there is generally provided a closed magnetic core which may be annular and on which is toroidally wound a length of wire to form a plurality of generally single-layer turns. A similar portion of each of the turns is shaped to provide a flat commutating surface and a brush is mounted for movement on the commutating surface to be in electrical engagement therewith such that at different positions of the brush on the commutating surface, a different value of output volt age is produced. This type of autotransformer while having particular advantageous characteristics has been found to be substantially limited with respect to the amount of electrical power that it may satisfactorily control. One limiting factor is that the temperature of the commutating surface at the locality where the brush engages it should not exceed a predetermined safe value but as the current between the brush and commutating surface increases, the temperature also increases and hence the latter serves as one factor to set the maximum current which may safely duces a substantially steplessly adjustable output voltage but yet which is capable of handling more power than has heretofore been possible.

Another object of the present invention is to provide in such an adjustable voltage autotransformer for increasing the current passing between the brush and commutator but yet maintaining the temperature thereat below its predetermined safe value.

A further object of the present invention is to provide an adjustable voltage autotransformer which achieves the above objects and yet which is readily manufacturable and relatively inexpensive for the amount of electrical power which it is capable of controlling.

In carrying out the present invention, there is provided a closed magnetic core which, as specifically shown hereafter, is annular through a closed rectangular core may be employed if desired. A winding of particular configuration, as hereinafter set forth, is toroidally wound on the core and a commutating surface is formed on the winding by flattening a common surface of each of the turns. A brush means is mounted for sliding movement on the commutating surface in electrical engagement with the turns and in accordance with the present invention includes at least two separate and distinct brushes with the output current flowing from the commutating surface through the brushes. The brushes are initially electrically isolated from each other but connected together by a reactor means that interconnects the two brushes to a common output and is in effect a paralleling transformer. The reactor means maintains a selected current density ratio between thebrushes to prevent one brush from trying to carry more than its'share of the total output current and hence it maintains the output current through ice each of the brushes at a selected proportion of the total output current.

The winding of the present invention consists of at least three parts, each of which constitutes an independent single length of conducting wire that is toroidally wound about the core. The three parts are wound as if they were one and thus when a commutating surface is formed on the turns of the winding there appears in sequentially repeating order a turn of the first part, a turn of the second part and a turn of the third part, a turn of the first part, second part, etc. The ends of the three parts are connected together in a manner which provides a substantially constant voltage differential between adjacent turns. Thus at any point on the commutating surface in the direction of brush movement for higher output voltage, there is provided a first turn part having a selected voltage, next a second turn part having a voltage equal to the selected voltage of the first turn part plus the differential voltage per turn, a third turn part having a voltage equal to the second turn part voltage plus the voltage differential between turns, then a first turn part having a voltage greater than the third turn voltage by the voltage differential between turns, etc.

In order to utilize such a winding to achieve the objects of the present invention the width of the brushes that contacts the conducting surfaces and the spacing between the brushes is such that at all times a turn of each of the parts is contacted by a brush and in some instances more than one turn of a part winding may be contacted.

Other features and advantages will hereinafter appear.

In the drawing:

FIG. 1 is a plan of an adjustable voltage autotransformer made according to the present invention.

FIG. 2 is an elevation, partly in section, thereof.

FIG. 3 is a diagrammatic and electrical schematic illustration of the autotransformer of the present invention.

FIG. 4 is an enlarged illustration of the commutating surface and brushes.

FIG. 5 is a pictoral and electrical schematic diagram of a further embodiment of the present invention.

FIG. 6 is similar to FIG. 5 of another embodiment of the present invention.

Referring to the drawing, the autotransformer is generally indicated by the reference numeral 10 and includes an annular core 11 which may be formed by spirally winding a flat strip of paramagnetic steel. The core is mounted in a frame 12 that also rotatably supports a shaft 13 on which is mounted a segmented brush arm 14 having a first part 1412 and a second part 14b. Each part 14a and 14b of the brush arm carries a brush 15a and 15b respectively at one end thereof for rotative movement with the shaft 13 that may be turned, as by a handwheel 16, about an arc of substantially 320.

Wound on the core 11 is a winding, generally indicated by the reference numeral 17, on which a commutating surface 18 is formed as by flattening or otherwise forming a fiat portion on a similar portion of each of the turns of the winding in the commutating surface. The brushes 15a and 15b are located on the brush arm 14 to ride on and be in electrical engagement with the commutating surface 18 as the latter is in the form of an arc while the brushes move arcuately.

In carrying out the present invention, the winding 17, in the specific embodiment of the invention shown in FIGS. 1 through 4, consists of a first part 19, a second part 20 and a third part 21, each of which is a single length of electrical conducting circular wire covered with a layer of electrical insulation. As schematically shown in FIG. 3, ends 1%, 20a and 21a of the winding parts are connected together and to an input terminal 22 and the other ends 19b, 20b and 21b are connected together and to another input terminal 23to place the winding parts 19, 20 and 21 in parallel between the input terminals. In winding the winding 17 on the core 11, the parts are wound as if they were a single wire winding and thus the commutating surface that is formed on the turns (FIG. 4) has sequentially repeating consecutive conducting surfaces 190, Ztlc, 21c; 190', Ne, 21c; 190", etc. with each of the conducting portions being formed on a turn of its part winding. Turns, as shown, are evenly spaced and thus the conducting surfaces have a definite distance between adjacent surfaces.

To provide for an increasing output voltage as the brush is moved along the commutating surface and for other hereinafter set forth purposes, adjacent conducting surfaces of the first winding part, ie 190, 190', 1%", are made to have a voltage differential therebetween which is substantially equal to the input voltage divided by the number of turns in this part winding and as each of the part turns has substantially the same number of turns there Will be a similar voltage existing between their adjacent conducting surf-aces. However, in order to provide a voltage differential between adjacent conducting surfaces of the winding, such as 190, 20c, 21c, 190', etc., the voltage that exists between adjacent conducting surfaces of winding parts is divided to appear between the adjacent conducting surfaces of the winding. Thus, for example, if a value of three volts exists between the conducting surfaces 190 and 19c of the winding part 19 and also 190 and 190 thereof, then the three volts are subdivided to cause a value of voltage between conducting surfaces 190 and 200 of the winding to be one volt, between conducting surfaces 200 and 210 to be one volt, and between 21c and we to be one volt, etc. In this manner as the brush moves over the commutating surface it engages conducting surfaces which have a substantially constant voltage increment between each conducting surface of the winding.

In the embodiment of the invention shown in FIGS. 1 through 4 the potential difference existing between the conducting surfaces of the winding is achieved by connecting the ends 19a, 20a and 21a to the input terminal 22 in a manner which causes the voltage difference to exist at the first conducting surfaces. This is effectuated by utilizing a voltage inducible in a partial turn wound around a core and thus the winding part end 19a extends through an aperture 19:! in the core to have a voltage induced therein equal to one-third the voltage existing between the conducting surfaces of the same part (i.e. 3 volts) while the end 26a of the winding part 20 extends through an aperture 20d in the core to enclose substantially two-thirds of the cross-section of the core and have induced therein a voltage which is equal to twothirds the differential voltage existing between the same conducting surfaces of a part winding. The end 21:: of the winding part 21 is wound completely around the core and thus has induced therein the voltage that does exist between adjacent conducting surfaces of the same winding part. The other ends 1%, 2% and 21b are wound in a similar manner to have two ends of the three be partial turns to accordingly provide the same number of turns in each windin g part.

It will thus be appreciated that on the end of the commutating surface at the input terminal 22 there is initially a conducting surface on the first turn of the winding part 19 that has a voltage value, in the example given, of one volt while the next conducting surface is formed on the first turn of the winding part 20 and has a voltage value of two volts and the next conducting surface is formed on the first turn of the winding part 21 and has a value of three volts. This relationship of voltage differential between adjacent conducting surfaces of each winding part and adjacent conducting surfaces of the winding 17 will exist throughout the length of the commutating surface. While the embodiment described specifically sets forth the first turn of each winding part, it will be appreciated that in some instances the commutating surface may not include the first turns but in any event the voltage differential relationships between adjacent conducting surfaces must be maintained throughout the conducting surface.

In accordance with the present invention, the brushes 15a and 15b are positioned in the output circuit to have the output current of the autotransformer flow therethrough. As shown in FIG. 3, the one output terminal 24 is connected to the input terminal 22 and another out put terminal 25 is connected to a center tap of a reactor 26, the latter consisting of a winding 27 wound on a magnetic core 28. One end 27a of the winding 27 is connected to the brush 15a and the other end of the winding 27 is connected to the brush 15b. With this structure it will be appreciated that the reactor 26 maintains the current density through each of the brushes 15a and 15!) substantially constant and equal as each produces substantially equal and opposing ampere turns in the core 23. If desired to have a greater current density in one brush or the other then the position of the connection of the output terminal 25 to the winding 27 would be changed to include more turns in one and less turns in the other.

Even though the brushes carry the same amount of current, the brushes are caused to have a shape and be spaced apart a distance which at all conducting positions thereof on the commutating surface cause at least a conducting surface of every winding part to be engaged by a brush. Referring to FIG. 4, it will be seen that the brush 15a has a surface 15a which engages the commutating surface 18 and the brush 'width 15a is equal to twice the center line distance or pitch between two conducting surfaces. Similarly the brush 15b has a surface 15b which is the same width as the surface 15a and also is capable of spanning completely two conducting surfaces engaging three surfaces but not engaging four surfaces. In addition, the spacing between the center lines of the surfaces 15a and 15b, indicated by the arrow X, is, in the embodiment specifically shown, equal to four and one-half times the pitch of the conducting surfaces but could also be 1 /2, 7 /2, 10 /2, 13 /2 times etc. or series 1 /2 plus 3 conducting surface pitches. In this manner no matter where the brushes 15a and 1511 are positioned on the commutating surface they will contact at least a part of a conducting surf-ace of every winding part.

As shown in FIGS. 1 and 2, if desired, the reactor may be annular and mounted on the frame 12 to circumscribe the shaft 13 within the central opening in the core 11 though of course it may be mounted on a separate frame or stand exterior of the core 11 if desire-d.

It will be appreciated that with this construction of an adjustable voltage autotransformer, that the current through each of the brushes maybe increased to that found most advantageous with respect to long life and performance of the autotransformer. As there are two brushes in the specific embodiment of the autotransformer 10, heretofore described, the total output current from such an autotransformer may be substantially doubled as compared to an autotransformer having only one brush with each of the brushes carrying the same value of current one alone may carry. In addition, by the use of multiple windings the brushes may be spaced apart in a manner which separates the localized heating occurring at each brush and thus the localized heating areas are not concentrated at a single area. The employment of the multiple winding parts additionally provides for a wider selection of the value of the differential voltage between adjacent conducting surfaces and thus aids in selecting a value of voltage which enables more effective control of the circulating current by the brush and contact resistance thereof with the commutating surface.

Shown in FIG. 5 is a pictorial and electrical schematic diagram of a further embodiment of the present invention in which an adjustable voltage autotransformer includes three brushes and a six-part winding. The autotransformer is generally indicated by the reference numeral 30 and includes a winding 31 wound on a closed magnetic core 32 with the winding having winding parts 31a through 31 inclusive. Input terminals 33 and 34 are connected to a primary winding 35 of a transformer 36 having two secondary windings 35a and 35b with each secondary winding 35a and 3511 being formed to provide six equally spaced taps 35a 35a and 35b-35b respectively. Each tap of the secondary winding 35a 35a is connectedto a beginning of a winding part and thus the tap 35a is connected to the winding part 31a, 35a to the winding part 31b, etc., while the other ends of the winding parts 31a-31f are similarly connected to equally spaced taps 355 -3515 on the'secondary winding 35]; as schematically shown. Additionally the input terminal 33 is connected to a center tap 33a of the winding 35a while input terminal 34 is connected to a center tap 34a on the winding 35b. The transformer 36 thus functions as the apertures 19d and 20d in the previous embodiment to provide a voltage differential of a selected value between adjacent contacting surfaces of the windings 31 and to have the same voltage across the whole of each winding part.

One output terminal 37 of the autotransformer 30 is connected to the input terminal 33 while another output terminal 38 is connected through a lead 39 to a tap 40 on a winding 41 of a reactor 42. One end 41a of the winding 41 is connected to a brush 43 while the other end 41b of the winding is connected to the midpoint of a Winding 44 of a reactor 45. The ends 4411 and 44b of the winding 44 are connected to brushes 46 and 47 respectively. It will be appreciated that with this construction that the brushes 46 and 47 are made to carry equal current by the reactor 45 and in order to cause the brush 43 to carry the same amount of current as either brush 46 or 47, the tap 40 on the winding 41 is placed such that two-thirds of the turns of the winding 41 carries the current from the brush 43 while the other one-third of the turns carries the current from the brushes 46 and 47.

As in the previously disclosed embodiment of the present invention, each of the turns of the windings 31 on which it is desired to commutate has a commutating surface 48 formed by conducting surfaces formed on the turns of the winding 31 with the conducting surfaces being sequentially repeating series of consecutive winding parts. Thus there are consecutive conducting surfaces 31a, 31b, 31c, 31d, 31c, 31 31a", 31b", 310", etc. that are substantially equally spaced defining the commutating surface 48 with a constant voltage difference between adjacent conducting surfaces. The surfaces of the brushes 47a, 46a and 43a that contact the commutating surface have a width which is substantially identical and wide enough to span at least two conducting surfaces. In addition, adjacent edges of the brushes are spaced apart for at least the length occupied by two adjacent conducting surfaces. In this manner, at all positions of the brushes 43, 46 and 47 on the commutating surface 48 at least a part of a conducting surface of every part winding is contacted and thus there is a flow of output current through each of the winding parts.

In some instances it has been found that the brush and contact resistance with the commutator when spanning two conducting surfaces may have a value which while maintaining the circulating current within limits may be too large with respect to the output current. To enable the circulating current between the two conductin-g surfaces to be maintained within limits and to decrease the brush and contact resistance to a lower value, the present invention includes the inserting of an impedance between the taps of the winding 35 and the beginning of each of the winding parts. Each of the impedances is of substantially identical value and thus there is provide-d, as specifically shown in the herein disclosed embodiment, a resistance 49a connected in series between the winding part 31a and the tap 35:1 a resistance 4% between tap 3541 and winding part 31b and similarly resistances 49c, 49d, 49a and 49 for the other taps and winding parts. There may also be provided at the other end of the winding parts, resistances connected between each of the winding parts and the taps of secondary winding 35b with these resistances being indicated by the reference characters 5011 through 50f inclusive. It will be appreciated that with such a construction, when a brush spans two adjacent conducting surfaces, that the path for the circulating current includes not only the brush and commutator contact resistance but also the resistance of one of the resistances 49 and one of resistances 50.

Shown in FIG. 6 is a further embodiment of the present invention of an adjustable voltage autotransformer, generally indicated by the reference numeral in which four brushes 61, 62, 63 and 64 are employed together with a six-part winding 65 having winding parts 65a through 65 inclusive. In the previously described embodiments of autotrans-formers 10 and 30, only one commutating surface was formed on the part of the winding at one end of the core while in the autotransformer 60, two commutating surfaces 66 and 67 are formed, one on each part of the winding at each end of the core. Also the brushes 61-64 may be mounted on a rotatably mounted shaft (such as the shaft 13) with a two-part brush arm (such as brush arm 14) at each end of the coil to maintain the proper spacing of the brushes and move them together.

Many parts of autotransformer 60 are identical to the embodiment of the invention shown in FIG. 5 and they are given the same reference characters. Accordingly there are input terminals 33 and 34, output terminals 37 and 38, transformer 36 having a primary winding 35 and secondary windings 35a and 35b each provided with taps 35:1 -35:1 inclusive and 35b 35b inclusive, respectively also resistances 49a through 49, inclusive and 50a through 50 inclusive are connected in the same manner as in autotransformer 30.

The commutating surface 66 is slidingly engaged by brushes 61 and 62 that are connected to a reactor 68 with the output from the two brushes appearing in a lead 69 connected to the center tap of the winding of the reactor 68. In addition, the commutating surface 67 is similarly slidingly engaged by brushes 63 and 64 connected to a reactor 70 with the output current therefrom appearing in a lead 71 connected to the center tap of the winding of the reactor 70. The leads 69 and 71 are connected to a third reactor 72 which is center-tapped as at 73 and connected to the output terminal 37. The brushes may be mounted on the shaft 13 on a brush arm similar to the brush arm 14a and 1412 if desired so long as they are electrically isolated and maintained at their selected spaced relationship for all positions thereof.

With this structure of an autotransformer it will be understood that the surfaces of the brushes which engage the commutating surface span at least two conducting surfaces formed on the turns to provide the commutating surfaces. In addition, the brushes are spaced such that at least a portion of every winding part is engaged by a brush either through the commutating surface 66 or surface 67. In this particular embodiment the brushes are spaced apart a distance equal to two and one-half conducting surfaces and thus in all instances at least one conducting surface is completely engaged by a brush though some brushes may engage one and one-half conducting surfaces.

It will accordingly be appreciated that there has been disclosed an adjustable voltage autotransformer which enables substantially stepless adjustment of the value of output voltage from substantially zero to maximum but yet is capable of controlling more electrical power than has heretofore been possible in such a type of autotransformer. This is achieved by the employment of a plurality of brushes, each of which only carries a portion of the total output power. The brushes are in sliding electrical contact with at least one commutating surface that is formed of conducting surfaces and are connected to the output of the autotransformer through reactor means which maintains the proportionate share of total output current flowing through the brushes. The conducting surfaces are formed on the surfaces of the turns of a multi-part winding and the brushes are spaced and have a width such that at all positions of the brushes, every winding part is in electrical engagement with at least one brush thereby assuring that output current flows through each part winding.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having a plurality of winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding parts, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces, and brush means including at least two electrically separated brushes mounted in spaced apart relationship to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of the winding parts for transferring current between said winding and said brushes.

2. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having a plurality of winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding parts, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces of the winding with a constant voltage appearing between adjacent conducting surfaces of the same winding part, and brush means including at least two electrically separated brushes mounted in spaced apart relationship to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of the winding parts for transferring current between said winding and said brushes.

3. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having a plurality of winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding parts, transformer means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces of the winding with a constant voltage appearing between adjacent conducting surfaces of the same winding part, said transformer means including impedances connected in series with each winding part to be in the circulating current path of a winding part, and brush means including at least two electrically separated brushes mounted in spaced apart relationship to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of the Wind ing parts for transferring current between said winding and said brushes.

4-. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having at least three winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding parts with there being a conducting surface of a first winding part turn between a conducting surface of a second winding part turn and a conducting surface of a third winding part turn, transformer means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces of the winding with a constant voltage appearing between adjacent conducting surfaces of the same winding part, said transformer means including impedances connected in series with each Winding part to be in the circulating current path of a winding part, and brush means including at least two electrically separated brushes mounted in spaced apart relationship to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of the three winding parts for transferring current between said winding and said brushes.

5. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having at least six winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces on the winding parts with there being consecutively arranged conducting surfaces of the first, second, third, fourth, fifth and sixth winding part turns, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces, and brush means including at least two electrically separated brushes mounted in spaced apart relationship to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of the six winding parts for transferring current between said winding and said brushes.

6. The invention as defined in claim 5 in which a second conducting surface is formed of each of the winding part turns having a conducting surface to form a second commutating surface and in which there are additional brush means mounted to move in electrical engagement on the second commutating surface.

7. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having a plurality of winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed .by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces, a substantially constant pitch distance existing between adjacent conducting surfaces of the winding, brush means mounted to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each winding part, said brush means being formed into two spaced and electrically insulated brushes with the brushes having a surface width that engages the commutating surface, the width of each of said brushes being at least as wide as twice the pitch distance existing between adjacent conducting surfaces and the identical parts of the brushes being spaced at least one and one-half times the pitch distance apart, and means connected to the brushes for maintaining a selected proportion of the total output current flowing through each brush.

8. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having a plurality of winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces, brush means mounted to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each winding part, said brush means being formed into at least three spaced and electrically insulated brushes with the brushes having a surface width that engages the commutating surface, and means connected to the brushes for maintaining a selected proportion of the total output current flowing through each brush, said means including a first reactor connected to two of the brushes and having an output and a second reactor connected to the output and the third brush and having an output which carries the total output current.

9. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having at least three winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding with there being a conducting surface of a first winding part turn between a conducting surface of a third winding part turn and a conducting surface of a second winding part turn, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces of the winding with a constant voltage appearing between adjacent conducting surfaces of the same winding part, a substantially constant pitch distance existing between adjacent conducting surfaces of the winding, brush means mounted to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each of said three winding parts, said brush means being formed into at least two spaced and electrically insulated brushes with the brushes having a surface width that engages the commutating surface, the width of each of said brushes being at least as wide as twice the pitch distance existing between adjacent conducting surfaces and identical points of the brushes being spaced at least one and one-half times the pitch distance apart, and means connected to the brushes for maintaining a selected proportion of the total output current flowing through each brush.

10. An adjustable voltage autotransformer comprising a closed magnetic core, a winding having at least six winding parts wound on said core to provide sequentially repeating immediately consecutive turns, a commutating surface formed by conducting surfaces of the turns to thereby provide sequentially repeating conducting surfaces of the winding with there being consecutively arranged conducting surfaces of the first, second, third, fourth, fifth and sixth Winding part turns, means for energizing the winding to provide a substantially constant incremental voltage difference between adjacent conducting surfaces, a substantially constant pitch distance existing between adjacent conducting surfaces of the winding, brush means mounted to move in electrical engagement on the commutating surface and engaging at least a conducting surface of each winding part, said brush means being formed into at least two spaced and electrically insulated brushes with the brushes having a surface width that engages the commutating surface, the Width of each of said brushes being at least as wide as twice the pitch distance existing between adjacent conducting surfaces and identical points of the brushes being spaced at least the pitch distance apart, and means connected to the brushes for maintaining a selected proportion of the total output current flowing through each brush.

11. The invention as defined in claim 10 in Which said brush means has three brushes electrically insulated and spaced from each other and said last-named means includes a first reactor connected to two of the brushes and having an output and a second reactor connected to the output and the third brush and having an output which carries the total output current.

12. The invention as defined in claim 10 in which a second conducting surface is formed of each of the winding turns having a conducting surface to form a second commutating surface, in which the brush means includes two additional brushes mounted to move in electrical en gagement on the second commutating surface, and in which the last-named means includes a first reactor connected to the two first-mentioned brushes and having an output, a second reactor connected to the two additional brushes and having an output and a third reactor connected to the output of the first reactor and the output of the second reactor and having an output which carries the total output current.

No references cited.

LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, Assistant Examiner, 

1. AN ADJUSTABLE VOLTAGE AUTOTRANSFORMER COMPRISING A CLOSED MAGNETIC CORE, A WINDING HAVING A PLURALITY OF WINDING PARTS WOUND OF SAID CORE TO PROVIDE SEQUENTIALLY REPEATING IMMEDIATELY CONSECUTIVE TURNS, A COMMUTATING SURFACE FORMED BY CONDUCTING SURFACES OF THE TURNS TO THEREBY PROVIDE SEQUENTIALLY REPEATING CONDUCTING SURFACES OF THE WINDING PARTS, MEANS FOR ENERGIZING THE WINDING TO PROVIDE A SUBSTANTIALLY CONSTANT INCREMENTAL VOLTAGE DIFFERENCE BETWEEN ADJACENT CONDUCTING SURFACES, AND BRUSH MEANS INCLUDING AT LEAST TWO ELECTRICALLY SEPARATED BRUSHES MOUNTED IN SPACED APART RELATIONSHIP TO MOVE IN ELECTRICAL ENGAGEMENT ON THE COMMUTATING SURFACE AND ENGAGING AT LEAST A CONDUCTING SURFACE OF EACH OF THE WINDING PARTS FOR TRANSFERRING CURRENT BETWEEN SAID WINDING AND SAID BRUSHES. 